1991 LEXUS SC400 check engine

DIAGNOSTIC CODE CLEARANCE
1. After repair of the trouble areas, the diagnostic code retainedin the ECU memory must be cleared out by removing the EFI
fuse (30A) from R/B No. 2 for 10 seconds or more, with the
ignition switch OFF.
HINT:
wCancellation can also be done by removing the battery
negative (±) terminal, but in this case, other memory
systems (clock, etc.) will also be cancelled out.
w If it is necessary to work on engine components
requiring removal of the battery terminal, a check must
first be made to see if a diagnostic code has been
recorded.
2. After cancellation, road test the vehicle to check that a normal
code is now read on the ºCHECKº engine warning light.
If the same diagnostic code appears, it indicates that the
trouble area has not been repaired thoroughly.
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ENGINE TROUBLESHOOTING Diagnosis SystemTR±13
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If a malfunction code is displayed during the diagnostic code check in tes\
t mode, check the circuit for that code
listed in the table below (Proceed to the page given for that circuit).
Tro ble Area
ºCHECKº EngineWarning Light *
Memory*See Page
Trouble AreaNormal
ModeTest
Mode
±±±±±±±±±±±±±±±±±±±±±±±±±±±±±
w Open or short in engine speed sensor, No. 1, No. 2
cam position sensor circuit.
w Engine speed sensor
w No. 1, No. 2 cam position sensor
w Starter
w ECU
ONN.A.TR±48
w Open or short in engine speed sensor circuit.w Oen or short in engine s eed sensor circuit.
w Engine speed sensor
ONN.A. Engine s eed sensor
w ECU
ONN.A.
w Open or short in engine speed sensor circuit.g
w Mechanical system malfunction (skipping teeth of
ti itiming
wbelt belt stretched)N.A.ONTR 52wbelt, belt stretched)
wEngine speed sensor
TR±52
w Engine s eed sensor
w ECU
w Mechanical system malfunction (skipping teeth ofw Mechanical system malfunction (ski ing teeth of
wtiming belt, belt stretched)ONNAwtiming belt, belt stretched)
w No. 1, No. 2 cam position sensorONN.A. No. 1, No. 2 cam osition sensor
w ECU
w Open or short in IGF1 circuit from igniter No.
1±ECU.
w Igniter No. 1
w ECU
ONN.A.TR±54
w Open or short in IGF2 circuit from igniter No.
2±ECU.
w Igniter No. 2
w ECU
ONN.A.TR±54
w ECUONN.A.XTR±61
w Open or short in heater circuit of main oxygen sen-
sor.
w Main oxygen sensor heaterONN.A.w Main oxygen sensor heater
w ECU
TR±62
w Main oxygen sensor circuit
w
Main oxygen sensorONONw Main oxygen sensor
*1, 2: See page TR±20.
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ENGINE TROUBLESHOOTING Diagnostic Code ChartTR±15
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ºCHECKº Engine
Tro ble Area
CHECK Engine
Warning Light *
Memory*See PageTrouble AreaNormal
ModeTest
ModeMemory* See Page
w Open or short in water temp. sensor circuit.
w Water temp. sensor
w ECU
ONONTR±68
w Open or short in intake air tempsensor circuitOFFw Open or short in intake air temp. sensor circuit.
w Intake air tempsensor
OFF
ONTR 72w Intake air temp. sensor
ECUON*3
ONTR±72
w ECUON*3
w Open or short in main oxygen sensor circuit.w Oen or short in main oxygen sensor circuit.
w Main oxygen sensor
Main oxygen sensor
w Ignition systemgy
w Water temp. sensor
w Open or short in injector circuit.w Oen or short in injector circuit.
w Fuel line pressure
(injector blockage)w Fuel line ressure (injector blockage)
w Air flow meter (air intake)ONONTR±74 Air flow meter (air intake)
w Engine ground bolt loose

gg
w Foreign object caught in valve
w Fuel line pressure (injector leak, blockage)w Fuel line ressure (injector leak, blockage)
w Mechanical system malfunction Mechanical system malfunction
w(skipping teeth of timing belt)(g g)
w Ignition system
w Open or short in heater circuit of sub±oxygen sen-
sor.
w Sub±oxygen sensor heaterONN.A.w Sub±oxygen sensor heater.
w ECU
TR±82
w Open or short in sub±oxygen sensor circuit.
TR 82
w Oen or short in sub oxygen sensor circuit.
w Sub±oxygen sensor
ONON Sub oxygen sensor
w ECU
w Same as (1) of Code No. 21ONN.A.
TR 62w Same as (2) of Code No. 21ONONTR±62
w Same as (1) of Code No. 27ONN.A.
TR 82w Same as (2) of Code No. 27ONONTR±82
*1, 2, 3: See page TR±20.
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ENGINE TROUBLESHOOTING Diagnostic Code ChartTR±17
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Trouble Area
ºCHECKº
Engine Warning
Light *

Memory* See PageTrouble Area
Normal
ModeTest
Mode
MemorySee Page
w Open or short in air flow meter circuit.
w Air flow meter
w ECU
ONN.A.TR±88
wECUONONTR±92
wOpen or short in throttle position sensor circuit.
wThrottle position sensorONONTR±94Throttle osition sensor
w ECU
wNo. 1 speed sensor
w Combination meter
w Open or short in No. 1 speed sensor circuit.
w ECU
ONONTR±98
wOpen or short in starter signal circuit.
w Open or short in ignition switch or main relay circuit.
w ECU
N.A.OFFXTR±100
wOpen or short in sub±throttle position sensor circuit.
wSub±throttle position sensorOFFONTR±94Sub throttle osition sensor
wECU
wOpen or short in No. 1 knock sensor circuit.wOen or short in No. 1 knock sensor circuit.
w No. 1 knock sensor (looseness)
ONN.A.No. 1 knock sensor (looseness)
wECU

w ECUONN.A.XTR±102
w Open or short in No. 2 knock sensor circuit.w Oen or short in No. 2 knock sensor circuit.
w No. 2 knock sensor (looseness)
ONN.A. No. 2 knock sensor (looseness)
w ECU

*1, 2: See page TR±20.
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ENGINE TROUBLESHOOTING Diagnostic Code ChartTR±19
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DIAGNOSTIC CODE CHART (Cont'd)
*1: ºONº displayed in the diagnosis mode column indicates that the º\
CHECKº Engine Warning Light islighted up when a malfunction is detected. ºOFFº indicates that the ºC\
HECKº does not light up during
malfunction diagnosis, even if a malfunction is detected. ºN.A.º i\
ndicates that the item is not included
in malfunction diagnosis.
*2: ºOº in the memory column indicates that a diagnostic code is reco\
rded in the ECU memory when a mal- function occurs. ºXº indicates that a diagnostic code is not recor\
ded in the ECU memory even if a mal-
function occurs. Accordingly, output of diagnostic results in normal or test mode is performed with \
the
IG switch ON.
*3: Only for USA specification vehicles.
TR±20
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ENGINE TROUBLESHOOTING Diagnostic Code Chart
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Trouble Area
ºCHECKº
Engine Warning
Light*

Memory* See PageTrouble Area
Normal
ModeTest
Mode
MemorySee Page
w Open or short in EGR step motor circuit.ONNA Oen or short in EGR ste motor circuit.
w ECUONN.A.
w Open in EGR gas temp. sensor circuit.ONON
TR±108 Oen in EGR gas tem . sensor circuit.
w ECUONON
w Open or short in fuel pump ECU circuit.
w Fuel pump ECU
w Engine & ECT ECU power source circuit.
w Fuel pump
w Engine & ECT ECU
ONONTR±114
w A/C switch circuit
w Throttle position sensor IDL circuit
w Neutral start switch circuit.
w Accelerator pedal and cable
w ECU
N.A.OFFXTR±118
*4: This indicates items for which º2 trip detection logicº is used. With this logic, when a lo\
gic malfunction is
first detected, the malfunction is temporarily stored in the ECU memory. If the same case is detected again
during the second drive test, this second detection causes the ºCHECK\
º Engine Warning Light to light up.
The 2 trip repeats the same mode a 2nd time. (However, the IG switch must be turned OFF between the
1st trip and 2nd trip).
In the Test Mode, the ºCHECKº Engine Warning Light lights up the 1st trip a malfunction is detected.
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ENGINE TROUBLESHOOTING Diagnostic Code ChartTR±21
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FAIL±SAFE CHART
If any of the following codes is recorded, the ECU enters fail±
safe mode.
Code No.Fail±Safe OperationFail±Safe Deactivation Conditions
14Fuel cut1 IGF1 detected in consecutive 8 ignitions.
15Fuel cut1 IGF2 detected in consecutive 8 ignitions.
16Torque control prohibited.Returned to normal condition.
22THW is fixed at 805C (176 5F).Returned to normal condition.
24THA is fixed at 20 5C (68 5F).Returned to normal condition.
31
Ignition timing controlled between 10 5 ~ 30 5
BTDC,
Injection time controlled between 3 msec. ~ 30 m
sec., in relation to:
w Engine rpm
w Throttle angle
w ISC step value
KS input 15 times/sec. or more.
35Atmospheric pressure is fixed at 760 mmHg.Returned to normal condition.
The following 1 or 2 must be repeated at least 2
times consecutively.
41VTA1 is fixed at 051 When IDL is ON41VTA1 is fixed at 051 When IDL is ON
0.25 V
VTA1
0.95 V
2 When IDL is OFF2 When IDL is OFF
0.25 V
VTA1
4.9 V
The following 1 or 2 must be repeated at least 2
times consecutively.
47Value of VTA1 is used1 When IDL2 is ON47Value of VTA1 is used.1 When IDL2 is ON
0.25 V
VTA2
0.95 V
2 When IDL2 is OFF2 When IDL2 is OFF
0.25 V
VTA2
4.9 V
52Max. timeing retardation.IG switch OFF.
53Max. timeing retardation.Returned to normal condition.
55Max. timeing retardation.IG switch OFF.
Back±Up Function
If there is trouble with the program in the ECU and the ignition signals\
(IGT) are not output, the ECU controls
fuel injection and ignition timing at predetermined levels as a back±up f\
unction to make it possible to continue
to operate the vehicle.
Furthermore, the injection duration is calculated from the satrting sign\
al (STA) and the throttle position signal
(IDL). Also, the ignition timing is fixed at the initial ignition timing, 5 5 BTDC, without relation to the engine speed.
HINT: If the engine is controlled by the back±up function, the CHECK ENGIN\
E light lights up to warn the driver
of the malfunction but the diagnostic code is not output. TR±22
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ENGINE TROUBLESHOOTING Fail±Safe Chart
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CHECK FOR MOMENTARY
INTERRUPTION
As described in the preceding paragraph, abnormality detection
ability in the test mode is increased compared to that in the normal
mode, so that when momentary interruptions or momentary shorts
occur in the ECU signal circuits (G1, G2, NE, THW, THA, VTA1,
VTA2) shown in the table below, the appropriate diagnostic code
is output.
Accordingly, when the diagnostic codes shown in the table below
(13, 22, 24, 41, 47) are output during the diagnostic code check,
and inspection of the appropriate circuits reveals no abnormality,
perform the check for momentary interruption as described below.
By performing the check for momentary interruption, the place
where momentary interruptions or momentary shorts are occur-
ring due to poor contacts can be isolated.
CLEAR DIAGNOSTIC CODES
See page TR±13.
SET TEST MODE
1. With the ignition switch off, using SST, connect the terminals
TE2 and E1 of the TDCL.
SST 09843±18020
2. Start the engine and check to see the ºCHECKº engine warning light to go off.
PERFORM A SIMULATION TEST
Using the symptom simulation (See page IN±20), apply vibration
to and pull lightly on the wire harness, connector or terminals in the
circuit indicated by the malfunction code.
In this test, if the ºCHECKº engine warning light lights up, it in\
di-
cates that the place where the wire harness, connector or termi-
nals being pulled or vibrated has faulty contact. Check that point
for loose connections, dirt on the terminals, poor fit or other prob-
lems and repair as necessary.
HINT: After cancelling out the diagnostic code in memory and set
the test mode, if the ºCHECKº engine warning light does not go off
after the engine is started, check thoroughly for faulty contact,
etc., then try the check again. If the ºCHECKº engine warning light
still does not go off, check and replace ECU.
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ENGINE TROUBLESHOOTING Check for Momentary InterruptionTR±23
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